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Optical coherence tomography assessment of capsule closure after cataract surgery

Sacu, Stefan MD; Findl, Oliver MD; Linnola, Reijo J. MD, PhD

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Journal of Cataract & Refractive Surgery: February 2005 - Volume 31 - Issue 2 - p 330-336
doi: 10.1016/j.jcrs.2004.04.057
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After cataract surgery with intraocular lens (IOL) implantation, the IOL initially locates centrally in the capsular bag as a result of the mechanical, spring-like force of the haptics. In the first days after surgery, the capsular bag collapses and contact between the anterior and posterior capsule leaflets begins in the equator region of the capsular bag. This fusion of the leaflets encroaches on the IOL optic rim. During this apposition process, the anterior capsulorhexis edge and posterior capsule come into contact with the optic surfaces of the IOL. This contact and the later-occurring bending of the posterior capsule at the posterior optic edge may be significant factors in the IOL's ability to inhibit the development of posterior capsule opacification (PCO). Subsequently, the capsule adheres to the IOL optic by extracellular matrix components such as fibronectin and laminin.1–3 Later, by transdifferentiation of anterior capsule lens epithelial cells (LECs) to myofibroblasts and laying down of collagen, the adhesion of the capsule to the optic becomes permanent.

The no-space, no-cells concept led to development of an IOL with a convex posterior surface that minimizes the space between the posterior capsule and the IOL optic. This concept implies that an IOL that causes early contact between the posterior capsule and IOL optic should lead to a lower incidence of PCO.4 In addition, a sharp optic edge induces a capsule bend that is thought to inhibit LEC migration and therefore PCO. Capsule bend formation seems to be key to understanding how some IOLs reduce the incidence of PCO.4,5 The sharpness of the bend and the speed of its formation seem to be important factors. The question is, when is the capsule bend created postoperatively? If it is created immediately or soon after surgery, LEC migration behind the IOL optic might be completely inhibited. If it develops later, LECs would likely migrate posteriorly before the capsule bend forms.4 Liu et al.6 report that the LEC growth and migration can be rapid. In their in vitro model, a confluent monolayer of LECs over the posterior capsule was seen after 5.8 days ± 0.6 (SD) in patients younger than 40 years and after 7.2 ± 0.7 days in patients older than 60 years. Thus, the time to capsule bend formation may be another important factor in the prevention of PCO by an IOL.

A reproducible documentation method is needed to compare the time course of capsule–optic contact and capsule bend formation between IOL types. It is possible to document the capsule–IOL interaction with slitlamp photography. However, standardization of this method is difficult and to our knowledge has not been attempted. Other techniques are Scheimpflug photography7–9 and ultrasound biomicroscopy.10 Optical coherence tomography (OCT) enables high-quality cross-section tomograms of the eye. Although it has been primarily used for performing tomography of the retina,11,12 it can also be used to scan the anterior segment and then measure the distances using the tomograms.

The aim of this study was to adapt OCT for the documentation and quantification of capsule–IOL contact and capsule bend formation in the pseudophakic eye after surgery. To determine the time to capsule–IOL contact with different IOL materials and designs, we periodically examined the status of the capsule using OCT.

Patients and Methods

Patient Recruitment and Lens Assignment

Thirty-three eyes of 33 patients with age-related cataract were included in this prospective clinical trial performed at the Department of Ophthalmology, Vienna General Hospital, Medical University of Vienna. The patients were recruited from a continuous cohort. All surgery was performed between June and November 2003. Exclusion criteria were a history of intraocular surgery, other ocular diseases, and a pupil diameter smaller than 6.5 mm after maximum dilation. All research and measurements followed the tenets of the Declaration of Helsinki.

The day before surgery, patients were randomly assigned to 1 of 3 groups based on IOL type: 1-piece acrylic (SA60AT, Alcon Surgical), 3-piece acrylic (MA60BM, Alcon Surgical), and 3-piece silicone (911A, AMO). Each group had 11 patients. All 3 IOL types have open-loop haptics, sharp-edged optics, an optic diameter of 6.0 mm, and an overall size of 13.0 mm. Table 1 shows the other characteristics of the IOLs.

Table 1
Table 1:
Material and design of the IOLs evaluated.

Surgical Technique

All patients were operated on by the same surgeon (O.F.) in the same fashion. Approximately 1 to 2 hours before surgery, diclofenac (Voltaren Ophtha), phenylephrine 2.5%–tropicamide 0.5% (Mydriaticum Agepha), and cyclopentolate 1% (Cyclopentolate Thilo) eyedrops were instilled. After topical anesthesia was administered, a temporal single-plane 3.2 mm posterior limbal incision was created. Hydroxypropyl methylcellulose 2% (Ocucoat) was then instilled in the anterior chamber. After a capsulorhexis was created and hydrodissection performed, phacoemulsification of the nucleus was done with the Oertli Orbit unit using a cracking technique. In all cases, the capsulotomy overlapped the IOL optic along its entire circumference. No attempt was made to polish the anterior capsule. The capsular bag was expanded with sodium hyaluronate 1% (Healon), after which the assigned foldable IOL was implanted in the bag with an injector system. The viscoelastic material was thoroughly aspirated from the retrolental space and the anterior chamber using an irrigation/aspiration (I/A) tip; the proximal edge of the IOL optic was tilted up with a spatula and the I/A tip inserted behind the optic. After the central portion of the viscoelastic material was removed, the residual material was removed by sweeping the I/A tip across and along the capsule equator. The I/A tip was guided into the anterior chamber and the optic repositioned. The incision was sutureless in all cases. Postoperative treatment comprised ketorolac tromethamine 0.5% (Acular) and dexamethasone gentamicin sulfate (Dexagenta POS) eyedrops 3 times a day for 1 month.

Image Acquisition and Data Evaluation

Examinations were performed 1 and 3 days and 1, 2, 3, and 4 weeks after surgery. At each follow-up, patients received phenylephrine 2.5% and tropicamide 0.5% at least 30 minutes before the examination.

All postoperative examinations included evaluation of the lens capsule and IOL by OCT (version 2010, Zeiss Humphrey Systems) by the same experienced examiner. Optical coherence tomography is a diagnostic imaging technique that uses low-coherence interferometry to produce cross-sectional tomograms of the ocular structures. A light source emits a beam of infrared light that is split between the eye and a reference mirror at a known spatial location. The “line group” script contained in the OCT software was used to perform the scans. The scan time was 1.0 second per scan and the scan length, between 2.8 mm and 3.2 mm. Patients were asked to fixate on a central green fixation target.

At the time the study was planned, data were available from retroillumination photographs of the angle between posterior capsule folds, or striae, and the line connecting the optic–haptic junctions. The mean angle between capsule folds and optic–haptic junction line from the retroillumination images was 109 ± 7 degrees for the SA60AT IOL, 66 ± 11 degrees for the MA60BM IOL, and 73 ± 4 degrees for the 911A IOL. To avoid performing OCT scans along capsule folds, the scan meridian was set perpendicular to the line connecting the optic–haptic junctions (Figure 1, top). Using the OCT 2 software, the distance between the anterior capsule and anterior IOL surface was measured at the capsulorhexis edge, the optic edge, and a point midway between the 2 (Figure 1, bottom). Then, the mean of the 3 measurements was calculated. The software calculates this distance for retinal tissue; thus, the value was transformed with the refractive index of aqueous (distance × 0.98, refractive index of aqueous=1.34; refractive index of retina=1.37) to determine the actual geometric distance.

Figure 1.
Figure 1.:
Top: The scan meridian is set perpendicular to the line connecting the optic–haptic junctions. Bottom: Using the OCT software, the distance between the anterior capsule and IOL surface is measured at the capsulorhexis edge (a), at the optic edge (b), and at a point midway between the 2 (c) (IOL = intraocular lens, OCT = optical coherence tomography).

The OCT images were used to determine the postoperative days on which the posterior capsule formed a bend at the posterior optic edge in the above-defined meridian and the posterior capsule was in complete contact with the optic. In some cases, it was difficult to clearly identify whether there was contact between the posterior capsule and the IOL during OCT scanning; this was mainly due to a reflex from the anterior vitreous face. In these cases, a slitlamp examination was performed by 2 examiners to resolve the uncertainty.

To study the intraexaminer short-term reproducibility of anterior capsule–IOL distance with OCT 2, 1 examiner performed 2 scans in 10 eyes with various IOLs (AcrySof MA60AC, MA60BM, and SA60AT [Alcon]; Z9000, [Pfizer]) not included in the study. The scans were taken 10 minutes apart after the OCT equipment was rebooted.

Statistical Analysis

The Kruskal-Wallis test was used to check for between-group differences in anterior capsule–IOL contact time, posterior capsule–IOL contact time, and capsule bend formation time. Pairwise comparisons between groups were calculated with the Wilcoxon 2-sample test. A P value less than 0.05 was considered statistically significant. The repeatability coefficient, defined as 1.96 × standard deviation, was used to describe intraexaminer reproducibility.13

Results

The mean age of the patients was 73 ± 12 years. Table 2 shows the patients' characteristics. There was no statistically significant difference between the 3 IOL groups in IOL power or patient age (P>.05). No surgical complications that led to patient exclusion occurred.

Table 2
Table 2:
Patients' characteristics.

On the first postoperative day, the anterior capsule was in contact with the IOL optic in 1 eye (9%) in the 1-piece acrylic group and in 2 eyes each (18%) in the 3-piece acrylic group and 3-piece silicone group. The posterior capsule was in contact with the peripheral part of the IOL optic in 3 eyes (27%), 5 eyes (46%), and 2 eyes (18%), respectively. The posterior capsule was in contact with the IOL on the same day or earlier than the anterior capsule in 28 eyes (85%). In all 3 IOL groups, capsule bend formation was noted earliest 7 days after surgery. Table 3 shows the postoperative day on which complete contact between the anterior and posterior capsules and the IOL optic as well as capsule bend formation were noted. There was a significant difference between the 1-piece acrylic group and 3-piece silicone group in time to capsule bend formation at the optic edge (P=.03); the mean time to capsule fusion was 10 days and 15 days, respectively. A hierarchical test order was used because multiplicity did not reach statistical significance, meaning that the significant difference may have been accidental. There were no significant differences between the 3 groups in contact time between the anterior capsule and IOL and between the posterior capsule and IOL (P>.05).

Table 3
Table 3:
Percentage of eyes with capsule contact postoperatively.

In the 1-piece acrylic group, the anterior capsule–IOL gap was 197 μm at 1 day, 80 μm at 3 days, and 8 μm at 7 days. At 2 weeks, the anterior capsule was in contact with the entire IOL optic edge in all eyes (Figure 2). Fusion of the posterior capsule peripheral to the IOL optic occurred within a mean of 3 days (range 1 to 7 days) and capsule bend formation at the optic edge, within a mean of 10 ± 6 days (range 7 to 21 days) (Figure 3).

Figure 2.
Figure 2.:
Time course of anterior capsule–IOL distance (P = piece).
Figure 3.
Figure 3.:
Mean days until capsule–IOL contact and capsule fusion (P = piece).

In the 3-piece acrylic group, the anterior capsule–IOL gap was 161 μm at 1 day, 58 μm at 3 days, and 25 μm at 7 days. At 2 weeks, the anterior capsule was in contact with the entire IOL optic edge in all eyes (Figure 2). Fusion of the posterior capsule peripheral to the IOL optic occurred within a mean of 4.5 days (range 1 to 14 days) and capsule bend formation at optic edge, within a mean of 13 ± 7 days (range 7 to 28 days) (Figure 3).

In the 3-piece silicone group, the anterior capsule–IOL gap was 220 μm at 1 day, 126 μm at 3 days, 40 μm at 7 days, and 15 μm at 14 days. In all eyes in this group, the anterior capsule came into contact with the entire IOL optic edge later (ie, after 3 weeks) than in the 1-piece acrylic and 3-piece acrylic groups (Figure 2). Contact between the peripheral posterior capsule and the IOL optic occurred within a mean of 7 days (range 1 to 14 days) and capsule bend formation at optic edge, within a mean of 15 ± 4 days (range 7 to 21 days) (Figure 3).

The correlation between the first and the second scan taken by the same examiner was excellent (r=0.99), showing reproducibility of OCT for measuring anterior capsule–IOL distance. There were no noteworthy outliers. The short-term intraexaminer reproducibility was high, with a mean difference of 3.4 μm and a maximum difference of 13.0 μm. The repeatability coefficient was 7.0 μm, meaning that scans of the same eye would be within this range in 95% of cases when the scans were taken by the same examiner.

Figure 4 shows representative cross-sectional tomograms from the data set.

Figure 4.
Figure 4.:
Representative postoperative cross-sectional tomograms of the 3 IOLs (P = piece). Upper row: At 1 day. Middle row: At 7 days. Bottom row: At 14 days. In the 1-piece acrylic group, there was no anterior capsule–IOL or posterior capsule–IOL contact at 1 day, there was contact between the IOL and the anterior and posterior capsules but no capsule bend formation at 7 days, and there was capsule bend at the capsule edge at 14 days. The results in the 3-piece acrylic group were similar except there was incomplete contact between anterior capsule and IOL at 7 days. The results in the 3-piece silicone group were similar to the results in the 1-piece acrylic group except there was no contact between anterior capsule and IOL.

Discussion

The results in our study demonstrate that there is no significant difference in anterior capsule–IOL distance and posterior capsule–IOL contact time between the 3 IOLs studied. However, capsule bend formation occurred later with the 3-piece silicone IOL than with the 1-piece acrylic IOL.

In this study, we used OCT to document and quantify capsule–IOL contact with good short-term reproducibility. The OCT technique was developed primarily to obtain cross-sectional tomograms of the posterior segment of the eye. However, it is also possible to perform cross-sectional tomograms of the anterior segment if the focus is changed accordingly. This method provides high-quality scans with good reproducibility and gives information on the anterior capsule–IOL gap and time to capsule closure. There was a short learning curve (about 10 patients) for attaining cross-sectional images of the anterior segment. However, we encountered problems with our scan method. A problem with the analysis method, as with most other imaging techniques, arises in eyes with a pupil diameter smaller than 6.5 mm after maximum dilation. It is not possible to perform cross-sectional scans behind the iris. The optical property of the cornea seems to be another influencing factor. Particularly in cases with tear-film problems, we had difficulty achieving high-quality cross-sectional tomograms in the early postoperative period, especially on the first day. Also, in some cases the signal from the anterior hyaloid membrane made it difficult to assess whether the posterior capsule was in contact with the IOL. In these cases, we distinguished between the capsule and IOL by slitlamp examination.

With all 3 IOL styles, capsule closure occurred 7 days postoperatively at the earliest and 28 days postoperatively at the latest. Two studies in the literature investigated the interaction between the lens capsule and IOL. Nishi and coauthors4 compared the state of the peripheral capsule with 3 IOLs of different optic materials (silicone, acrylic, and poly(methyl methacrylate) [PMMA]) and found that capsule bend formation was complete 1 month after surgery with the foldable IOLs (AcrySof; PhacoFlex II SI-40NB, Allergan) but was significantly delayed with the PMMA IOL (UV26T, Menicon). Adhesion of an acrylic optic to the capsule has been reported to be stronger than adhesion of silicone.3,14–16 Hayashi and coauthors17 also examined contact between the entire capsule (anterior and posterior surfaces) and the IOL optic in eyes with a 3-piece silicone (SI-40NB) and a 3-piece acrylic IOL (MA60BM). They found capsule contact with the IOL optic was complete within approximately 8 days after cataract surgery with the silicone IOLs and within 11 days with the acrylic IOLs and that complete contact with both the anterior and posterior capsules occurred significantly earlier with the silicone IOLs than with the acrylic IOLs. In our study, there was a difference between the 1-piece acrylic group and 3-piece silicone group in the time to capsule bend formation (10 days and 15 days, respectively). However, the IOLs in our trial were different than those examined by Hayashi and coauthors. The material of the IOL optic as well as the style of haptics influenced our outcome. There were no significant differences between the 3 groups in contact time between the anterior capsule and IOL and between the posterior capsule and IOL.

Hayashi and coauthors17 describe 3 stages of capsule bend formation. In stage 1, immediately after implantation, the IOL is only weakly supported by the haptics in the capsular bag. In stage 2, the anterior and posterior capsules came in contact with the IOL, mechanically stabilizing it. In stage 3, fibrous tissue and LECs firmly adhere to the IOL, effecting final fixation. Nishi and coauthors4 divided the postoperative capsule bend formation into 5 stages. In stage 0, there is no adhesion between the anterior capsule and IOL. In stage 1, there is adhesion between the anterior capsule and IOL. In stage 2 there is adhesion between the anterior and posterior capsules peripherally, which progresses toward the optic edge in stage 3. In stage 4, the posterior capsule wraps around the optic edge. In the present study, we observed the following stages: (1) contact between the anterior and posterior capsules peripherally and contact between the posterior and anterior capsules and the IOL at the same time; (2) progression of capsule contact toward the optic edge; (3) capsule bend formation, in which the fusion line stays open in the area of the optic–haptic junction.

Some factors, such as optic edge design; optic thickness and size; haptic shape, size, and angulation; and capsule size, may influence the rate of capsule bend formation. Another influencing factor may be surgical technique. If the viscoelastic material is not completely removed from the retrolental space, a delay in capsule closure can be expected. In our study, the aspiration opening was rotated to the right, the left, or posteriorly; the viscoelastic material was circumferentially and thoroughly removed from behind the IOL and from the equator of the capsular bag. Also, if another meridian for OCT scanning had been chosen, the outcome of our study may have been different. Capsule bend formation along the entire optic circumference does not seem to proceed at the same speed. Therefore, whether the optical coherence tomographer scans at different meridians and thus results in different outcomes remains open to question.

In conclusion, OCT image acquisition and scan analysis allowed standardized documentation and quantification of anterior capsule–IOL distances. The technique produced cross-sectional tomograms of capsule–IOL contact in the early postoperative period with a short learning curve and very high reproducibility. To compare anterior capsule–IOL distance with the 3 IOL types, we took OCT scans in a meridian perpendicular to the line connecting the optic–haptic junctions. Using this method, we did not find significant differences in anterior capsule–IOL distance and posterior capsule–IOL contact time between the IOLs. However, capsule bend formation occurred later with the 3-piece silicone IOL than with the 1-piece acrylic IOL.

References

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© 2005 by Lippincott Williams & Wilkins, Inc.